Shanghai Institute of Optics and Fine Mechanics,Chinese Academy of Sciences
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Microwave interrogation cavity for the rubidium space cold atom clock
No full textNational Natural Science Foundation of China [11034008]; Fund from the Ministry of Science and Technology of China [2013YQ09094304]; Youth Innovation Promotion Association, Chinese Academy of SciencesThe performance of space cold atom clocks (SCACs) should be improved thanks to the microgravity environment in space. The microwave interrogation cavity is a key element in a SCAC. In this paper, we develop a microwave interrogation cavity especially for the rubidium SCAC. The interrogation cavity has two microwave interaction zones with a single feed-in source, which is located at the center of the cavity for symmetric coupling excitation and to ensure that the two interaction zones are in phase. The interrogation cavity has a measured resonance frequency of 6.835056471 GHz with a loaded quality factor of nearly 4200, which shows good agreement with simulation results. We measure the Rabi frequency of the clock transition of the rubidium atom in each microwave interaction zone, and subsequently demonstrate that the distributions of the magnetic field in the two interaction zones are the same and meet all requirements of the rubidium SCAC
Observation of fundamental thermal noise in optical fibers down to infrasonic frequencies
No full textNational Natural Science Foundation of China [11034008, 11274324]; Key Research Program of the Chinese Academy of Sciences [KJZD-EW-W02]The intrinsic thermal noise in optical fibers represents the ultimate limit for fiber-based systems. However, at infrasonic frequencies, the spectral behavior of the intrinsic thermal noise is still unclear. In this letter, we present measurements of the fundamental thermal noise in optical fibers that are obtained using a balanced fiber Michelson interferometer. When an ultra-stable laser is used as the laser source and other noise sources are carefully controlled, the 1/f spectral density of the thermal noise is observed down to infrasonic frequencies, and the measured magnitude is consistent with the results of theoretical predictions at frequencies over the range from 0.2 Hz to 20 kHz. Moreover, as observed experimentally, the level of the 1/f thermal noise can be reduced by changing the coatings of the optical fibers. This therefore indicates one possible way to reduce thermal noise in optical fibers at low Fourier frequencies. Finally, the inconsistency between the experimental data and the existing theory for thermomechanical noise is discussed. (C) 2016 AIP Publishing LLC
Probe Laser Power Stabilization for Integrated Sphere Cold Atom Clock
No full text建立了微瓦量级的激光功率自动稳定实验装置,通过自动反馈控制声光调制器的衍射效率,实现了激光功率的自动稳定。激光功率稳定后,激光相对强度噪声得到有效抑制,接近散弹噪声极限,激光功率的长期稳定度优于2*10~(-5)(1000s)。推导了功率自动稳定系统的环路方程,分析了激光功率稳定环路对相对强度噪声的抑制作用。稳定后的激光应用于积分球冷原子钟的钟跃迁探测,对原子钟稳定度的影响小于1*10~(-13)tau~(-1/2),积分球原子钟的频率稳定度优于5*10~(-13)tau~(-1/2)(tau为取样时间)国家863计划A laser power stabilization system for themuW probe laser is developed.Power stabilization is realized by automatically adjusting diffraction efficiency of the acousto-optic modulator.The relative intensity noise of the probe laser is effectively suppressed to the shot noise limit,and the long-term stability is better than 2*10~(-5)(1000s). The loop function equation of the power stabilization system is deduced,and the suppression effect of the loop on the relative intensity noise is analyzed.The stabilized laser is applied to detecting the clock transition of the integrating sphere cold atom clock,and its contribution to the frequency stability is less than 1*10~(-13)tau~(-1/2)(tauis the samping time).The frequency stability of the clock is improved to better than 5*10~(-13)tau~(-1/2)
Robust spatial coherence 5 mu m from a room-temperature atom chip
No full textIsrael Science Foundation [1381/13]; European Commission "MatterWave" consortium [FP7-ICT-601180]; German-Israeli DIP project - Deutsche Forschungsgemeinschaft [FO 703/2-1]; PBC program for outstanding postdoctoral researchers of the Council for Higher EdWe study spatial coherence near a classical environment by loading a Bose-Einstein condensate into a magnetic lattice potential and observing diffraction. Even very close to a surface (5 mu m), and even when the surface is at room temperature, spatial coherence persists for a relatively long time (>= 500 ms). In addition, the observed spatial coherence extends over several lattice sites, a significantly greater distance than the atom-surface separation. This opens the door for atomic circuits, and may help elucidate the interplay between spatial dephasing, interatomic interactions, and external noise
Three wire toroidal magnetic guide based on the vertical leads and ac current modulation
No full text提出了一种在单层原子芯片上实现闭合且导引中心无磁场零点的环形磁导引的新方案.芯片表面刻蚀的导线结构由同心等距三环线构成,三环线的电流引线垂直于芯片表面.加载直流电流后,这种构型即可在芯片表面附近产生闭合的环形磁导引.交流调制三环线电流后,环形磁导引的势能极小值附近不再存在磁场零点且其磁场起伏小.这种方案可用于基于物质波干涉的原子芯片陀螺仪研究.A new scheme to create a closed toroidal magnetic waveguide for deBroglie wave on a single layer atom chip is proposed and there is no zero magnetic field along the guide center. The guide is a two-dimensional magnetic trap for trapping weak-field seeking states of atoms with a magnetic dipole moment. The designed wire structure on the atom chip consists of three concentric and isometric ring wires, and six vertical current leads of the three ring wires. By using the through silicon via technology, the current leads can be made perpendicular to the atom chip surface instead of being generally arranged side by side on the chip surface. Compared with the general wiring way, the vertical lead way has two advantages. One is that each ring wire gap caused by the current leads is substantially smaller than the distance between the ring wires, which permits the generation of a closed toroidal magnetic guide near the atom chip surface when dc currents are supplied to the three ring wires. The other is that the distance between two leads of each ring wire is considerably reduced, resulting in the fact that the magnetic perturbation of the leads to the whole toroidal magnetic guide is negligible. We numerically calculate the magnetic field distribution generated by our wire layout when dc currents are applied, and it is shown that a closed and tight toroidal magnetic guide is formed near the atom chip surface. However, there are zero magnetic fields existing along the center of the toroidal guide, which leads to Majorana spin flips from trapped magnetic substate to an un-trapped magnetic sub-state. According to the time-orbiting-potential principle, we propose an ac current modulation method, which is simple and stable, to reduce the atom losses and suppress the atomic decoherence in the toroidal magnetic guide. We deduce the ac current expressions for the case of three isometric infinite straight wires and apply the ac modulation current expressions directly to our three ring wire structure. The numerical calculation results show that the closed toroidal guide does no longer have zero magnetic fields near the magnetic field minimum, and that the magnetic field fluctuation of the guide is smaller. Based on the vertical leads and ac current modulation, the closed toroidal wave guide with no zero magnetic field along the guide center can be generated near the atom chip surface. This scheme has important scientific significance and engineering value for developing the cold atomic chip gyroscope
Attenuation of high rate in parameter measurement of high power laser
No full text在高功率激光参数测量中,高倍率衰减方案设计是空间分布测量的关键。分析了远场测量光学系统,将95%环围能量直径作为评价远场测量系统的重要指标,明确了高倍率衰减对远场测量结果的影响,确立了高倍率衰减方案的设计原则。利用Virtual Lab软件,针对单个平板、成对平板、成对楔板三种常见的高倍率衰减方案,分析了衰减片摆放角度、位置、厚度、成对衰减片间距等因素对于远场测量系统的影响。针对焦距3 000 mm,F数为10的缩束系统,考虑杂散光对于远场测量的影响,优化得出最佳高倍率衰减方案。该方案下,远场像面处95%In high power laser beam parameters measurement, attenuation scheme with high rate is key to far-field measurement. The far-field optical measurement system was analyzed and diameter of 95% encircled energy was used as important evaluation criterion of far-field measurement system. Measurement error of far-field optical measurement system and effect of attenuation with high rate on far-field measurement results were analyzed. Principle of attenuation scheme with high rate was established. By changing parameters of high attenuation rate in condition of single parallel plate, a pair of parallel plates and a pair of wedge flaps by Virtual Lab, influence of attenuation on the far-field measurement system was simulated and analyzed deeply. According to measurement system for f =3 000 mm and F =10, best attenuation scheme with high rate is designed. Diameter of 95% encircled energy of far-field image is 45.5 μm, or 3.54 times of diffraction limitation. ? 2016, Editorial Board of Journal of Infrared and Laser Engineering. All right reserved
High Power Laser Multi-Parameter Measurement Technique Based on Integrating Sphere
No full text针对传统测量技术对入射光入射方向敏感的缺点,提出了一种基于积分球的高功率激光多参数测量的分光技术。采用蒙特卡罗法对衰减率、出射光时间波形特性、入射光时间波形恢复这三个方面进行了数值分析和仿真,验证了积分球作为激光测量系统中的分光元件的可行性。利用积分球对纳秒激光的能量和时间波形进行测量,实验结果与理论分析相符。实验与仿真均表明在激光参数测量中采用该分光技术,通过测量出射光各项参数可以恢复入射光的光谱参数、能量参数、时间参数,克服传统技术中入射光的入射方向对于出射光的各项参数有较大影响的问题。该技术方案占用Aiming at the disadvantage that the traditional measurement technique is sensitive to the incident direction of incident light, a beam-split technique of high power laser multi-parameter measurement based on integrating sphere is proposed. Numerical analysis and simulation about attenuation rate, time waveform of emergent light, and time waveform recovery of incident light are carried out by Monte-Carlo method, which validate the feasibility that the integrating sphere can be used as beam-splitter in laser measurement system. The energy and time waveform of nanosecond laser is measured based on integrating sphere. The theoretical analysis matches well with the experiment result. Experiment and simulation results show that spectrum parameter, energy parameter and time parameter of incident light can be recovered by measuring the parameters of the emergent light, when the light-split technique is used in laser parameters measurement. The proposed technique can conquer the disadvantage that the incident direction of incident light has great influence on the parameters of the emergent light in traditional technique. The proposed technical proposal possesses small volume and is easy to integrate, which can be used in modular design of multiple beam high power laser parameters measurement system
Multichannel optimal control algorithm for adaptive optics system
No full textNational Natural Science Foundation of China [11403079]In this paper we propose a multichannel optimal control algorithm (MOCA) which can be applied to practical real-time closed-loop adaptive optics system (AOS). The MOCA, doesn't like the traditional ones, considers both the effect of atmospheric turbulence and of the time delay. The control parameters are optimized timely through iterative calculations in order to let the system working at the best controlling state. Here we study, by the means of numerical simulations, the multichannel optimal control method with Recursive Least Square (RLS) algorithm, considering a 61-element AOS as an example. Analyses were made on convergence, control performance and bandwidth of this algorithm. Compared with the classical optimal proportional-integral control algorithm, simulation results show that the residual error caused by the atmospheric turbulence and servo lag in the system are reduced more effectively by using MOCA which has good adaptability and could improve the close-loop bandwidth of the AOS. (C) 2016 Elsevier GmbH. All rights reserved
On-shot laser beam diagnostics for high-power laser facility with phase modulation imaging
No full text[GFZX0205010502.12]; [CXJJ-14-S104]A coherent-modulation-imaging-based (CMI) algorithm has been employed for on-shot laser beam diagnostics in high-power laser facilities, where high-intensity short-pulsed lasers from terawatt to petawatt are designed to realize inertial confinement fusion (ICF). A single-shot intensity measurement is sufficient for wave-front reconstruction, both for the near-field and far-field at the same time. The iterative reconstruction process is computationally very efficient and was completed in dozens of seconds by the additional use of a GPU device to speed it up. The compact measurement unit-including a CCD and a piece of pre-characterized phase plate-makes it convenient for focal-spot intensity prediction in the target chamber. It can be placed almost anywhere in high-power laser facilities to achieve near-field wave-front diagnostics. The feasibility of the method has been demonstrated by conducting a series of experiments with diagnostic beams and seed pulses with deactivated amplifiers in our high-power laser system
Research Status and Development Trend of PIE Imaging Method
No full text作为一种新近发展的无透镜成像技术,PIE(ptychographical iterative engine)不但保持了传统相干衍射成像方法装置简单、使用方便等优点,克服了视场受限和收敛速度慢等缺点,还具有成像范围可扩展、收敛速度快、抗噪声能力强等优势,在光学、X射线和电子束等领域得到了广泛关注并开展了大量研究,是一种有可能在大范围内替代现有相位成像技术的新方法。主要介绍了PIE方法的技术背景、技术现状、相关应用及面临的问题和可能的发展方向。中科院百人计划As a newly developed lensless imaging technique,PIE(ptychographical iterative engine)does not only maintain the simplicity and convenience of the equipment of traditional coherent diffraction imaging (CDI)methods,but also overcomes the drawbacks such as restricted field of view and slow convergence.With the extensible imaging field,better convergence speed and higher immunization capability to noise,PIE is widely researched and used in optical,X-ray and electron beam imaging fields.PIE is a new method which is possible to replace the current phase imaging methods.The background,development,applications,problems and developing trend of the PIE method are introduced